The disclosure relates to a method and a device for quantifying in particular a wear-induced leakage flow on a process control valve of a process field device that restricts a process stream, in particular with a constant stream pressure, wherein the process control valve is in the closed position.
During wear diagnosis, methods and process engineering is limited to identifying a leakage on a process control valve, for example by detecting when a no longer acceptable leakage state has been exceeded. Further information about wear progression as well as predictions of wear development can only be arrived at with complicated and expensive detection technology.
Process control valves, such as positioning valves or emergency check valves, are exposed to a stream of process fluid, which exhibits a varying composition depending on the process technology. A process fluid stream with a high percentage of solids causes more wear to the flow-regulating control valve. A wide variety of operating phenomena, such as corrosion, abrasion, cavitation or flashing, can also lead to increased wear on the valve unit. A worn valve unit of the control valve is first and foremost no longer able to sufficiently cut off the stream of process fluid. The leakage can result in a loss of product, and hence in a less efficient process, or in a safety risk to the entire system. Monitoring the leakage above all during operation of the process technology system is very important with respect to the operability and reliability of the actuator in the process technology system.
Literature about process technology involving control valves envisages solution approaches in which the so-called internal leakage in actuators is to be detected. Proposed in the article “Detektion der Innenleckage von Stellgeräten” (“Detection of Internal Leaks in Actuators”) authored by Jörg Kiesbauer and Heinfried Hoffman (journal atp 42 (2000), issue 11) is a detection method in which a mechanical vibration sensor and positioner are used to acquire the presence or absence of smaller flow rates owing to the internal leakage.
Known from DE 10 2007 045 529 A1 is a diagnosis method for a control valve, such as a closing valve. In a first step, the stream pressure on the inlet line of the control valve is determined and compared with a first reference value corresponding to a family of characteristics or characteristic lines whose parameters are the Kv value and leakage class of the valve. In a second step, the mechanical vibration level is measured and compared with a second reference value, which is determined during startup as the sound level during the transition of a turbulent stream into a cavitation-affected stream. The known diagnosis method realizes a threshold-values analysis for the leakage situation.